変更に追従する：Observer #75

・5.2 通知を受けるよりよい方法

EFROR-62

app/domains/design_pattern/observer/employee.rb

@@ -4,17 +4,31 @@ class Employee
             attr_reader :name
             attr_accessor :title, :salary
 
-            def initialize(name, title, salary, payroll)
+            def initialize(name, title, salary)
                 @name = name
                 @title = title
                 @salary = salary
-                @payroll = payroll
+                @observers = []
             end
 
             def salary=(new_salary)
                 @salary = new_salary
-                @payroll.update(self)
+                notify_observers
+            end
+
+            def notify_observers
+              @observers.each do |observer|
+                observer.update(self)
+              end
+            end
+
+            def add_observer(observer)
+              @observers << observer
+            end
+
+            def delete_observer(observer)
+              @observers.delete(observer)
             end
         end
     end
-end
+end

app/domains/design_pattern/observer/tax_man.rb

@@ -0,0 +1,9 @@
+module DesignPattern
+    module Observer
+        class TaxMan
+            def update( changed_employee )
+                puts("#{changed_employee.name}に新しい税金の請求書を送ります！")
+            end
+        end
+    end
+end

spec/domains/design_pattern/observer/employee_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+
+describe DesignPattern::Observer::Employee do
+  describe '#salary' do
+    it 'observe payroll' do
+      fred = DesignPattern::Observer::Employee.new('Fred', 'Crane Operator', 30000)
+      payroll = DesignPattern::Observer::Payroll.new
+      fred.add_observer( payroll )
+
+      expected = <<-EOS
+Fredのために小切手を切ります！
+彼の給料はいま35000です！
+      EOS
+
+      expect { fred.salary = 35000 }.to output(expected).to_stdout
+    end
+
+    it 'observe payroll and tax man' do
+      fred = DesignPattern::Observer::Employee.new('Fred', 'Crane Operator', 30000)
+      payroll = DesignPattern::Observer::Payroll.new
+      fred.add_observer( payroll )
+      tax_man = DesignPattern::Observer::TaxMan.new
+      fred.add_observer( tax_man )
+
+      expected = <<-EOS
+Fredのために小切手を切ります！
+彼の給料はいま90000です！
+Fredに新しい税金の請求書を送ります！
+      EOS
+
+      expect { fred.salary = 90000 }.to output(expected).to_stdout
+    end    
+  end
+end